It is the latest contamination problem to hit Europe after a similar case in 2004, when dioxin, a class of chemicals widely used in industrial processes, was found in Dutch potato feed.

"This incident has an impact not only on the quarantined farms, but the whole livestock breeding industry. Sales are stagnating as a result of import bans... and damage to trade is rising rapidly," the main Dutch farmers' organisation LTO said in a statement.

"The damage to our reputation is also considerable. This not acceptable for us," it said.

South Korea banned pork meat from Belgium and the Netherlands, one of the world's top meat exporters, some two weeks ago when news about the dioxin contamination first broke.

LTO said the existing rules on controlling animal feed were not enough to guarantee their safety and urged the Dutch feed makers association Nevedi to come up with a proposal soon on how to prevent future incidents.

COMPLIANCE WITH RULES

Nevedi, however, said the problem did not lie with the rules but in their implementation, adding authorities should do more to make sure companies, which provide raw materials to the feed industry, comply with the standards.

"It is very annoying given the impact it is having on our industry," Wil van de Fliert, Nevedi's chairman, told Reuters.

"It is not a question of having a system (of rules and preventive measures) as the system is in place, but it is a question of people not complying with it," he said.

A spokeswoman for the Dutch food safety authority VWA declined to comment. VWA says on its website that safety measures taken by the EU and the government have increasingly reduced the number of dioxin incidents in the past several years.

VWA said in a statement later on Monday that it had reopened another 42 pig farms after meat test results were favourable. It expects more results later in the week as 159 out of the initially 250 quarantined farms remain shut.

Contaminated feed has triggered several west European food scares such as the discovery of dioxin in Dutch potato animal feed in 2004, an illegal hormone in Dutch pigs in 2002 and a 1999 Belgian scandal of dioxin in chickens.

Authorities have said that the dioxin in the latest incident got into Belgian pork fat ingredients used to make animal feed in October. It was discovered and announced in late January.

Belgian food safety officials have said the contamination was caused by broken filters which led to the use of unfiltered ingredients to extract pig fat from the process of making gelatine at Belgian firm PB Gelatins.

The extracted fat was later distributed to Belgian animal feed producers such as Leroy and Algoet. Shares in Belgian chemical firm Tessenderlo, which owns PB Gelatins, fell last week on the dioxin news.

The EU said on Friday it planned to tighten its rules on toxic chemicals like dioxins in food and animal feed, hoping to avoid a repeat of the latest scare in the three EU countries.